Method of manufacturing tissue sealing electrodes

ABSTRACT

An electrode assembly for use with an electrosurgical instrument includes a pair of opposing jaw members and an electrode positioned on each jaw member. One or both of the electrodes includes a tissue contacting surface that has an outer periphery and defines a side surface depending therefrom. The tissue contacting surface and the side surface include a conjoining edge formed at a first predetermined angle that defines a first linear transition zone dimensioned to reduce arcing between the opposing jaw members during activation of the electrosurgical instrument.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of U.S. patentapplication Ser. No. 14/273,350, filed on May 8, 2014, which is acontinuation application of U.S. patent application Ser. No. 12/861,198,filed on Aug. 23, 2010 (now U.S. Pat. No. 8,814,864), the entirecontents of which are incorporated by reference herein.

BACKGROUND Technical Field

The present disclosure relates to electrosurgical instruments used foropen and endoscopic surgical procedures. More particularly, the presentdisclosure relates to a method of manufacturing tissue sealingelectrodes for sealing vessels and vascular tissue.

Description of Related Art

Monopolar and bipolar instruments are among the most commonly utilizedinstruments in the field of electrosurgery. Briefly, monopolarinstruments utilize one or more active electrode(s) that are associatedwith a clamping electrode (e.g., jaw members) and a remote patientreturn electrode or pad that is attached externally to the patient.Bipolar electrosurgical forceps utilize two generally opposingelectrodes. Both electrodes are generally disposed on an inner facing oropposing surfaces of the jaw members, which are, in turn, electricallycoupled to an electrosurgical generator.

Essentially, during monopolar surgical treatment, energy travels fromthe active electrode(s) to the surgical site, through the patient and tothe return electrode or pad. In the situation where more than oneelectrode is utilized, all of the active electrodes are charged to thesame electric potential. On the other hand, during bipolar surgicaltreatment, each opposing electrode is charged to a different electricpotential. Since tissue is a conductor of electrical energy, when theelectrodes are utilized to clamp or grasp tissue therebetween, theelectrical energy can be selectively transferred from one electrode tothe other electrode, through the tissue, to effectively seal the tissue.

The construction and mechanics of surgical electrodes both play a majorrole in affecting a proper seal with tissue and vessels, especiallylarger vessels. For example, the seal quality may be affected by thepressure applied to the vessels and/or the sealing area of theelectrodes. Accordingly, the rate and effectiveness at which tissueand/or vessels are sealed depends on the jaw pressure and the sealingarea (e.g., surface area of electrode) of the jaw members. With thisconcept in mind, a larger jaw requires more energy to compensate for thegreater surface area, alongside with the greater amount of tissue beingclamped or grasped by the larger jaw members. However, in larger jawmembers, when the pressure is sufficiently increased, lesselectrosurgical energy is required. This is evidenced by the bioheatequation and the Arrhenius function, which confirms that temperature isrelated to surface area and tissue heating becomes a function oftemperature with respect to time, as shown below in the bioheat equation(1):

$\begin{matrix}{T = {{\frac{1}{\sigma \; \rho \; c}*J^{2}t} + T_{0}}} & (1)\end{matrix}$

where “T” is temperature, “σ” is Stefan-Boltzmann constant, “ρ” isdensity of tissue, “c” is the specific heat of tissue, “J” is thecurrent density and “t” is time. It is important to note that currentdensity depends on the area through which current is conducted. Forexample, a small area can amplify the effect of current on temperature.

As discussed above, tissue heat is calculated using the Arrheniusfunction (2) shown below:

$\begin{matrix}{\Omega = {\int{A\; e^{({\frac{- {Ea}}{R}*\frac{1}{T}})}{dt}}}} & (2)\end{matrix}$

where “Ω” is a dimensionless burn parameter (e.g., Ω=1 means firstdegree burn), “A” is a frequency factor, “E” is the activation energy,“R” is the universal gas constant, and “T” is tissue temperature.

With reference to the equations (1) and (2), the sealing quality oftissue (with respect to current density delivered over time) and thetemperature of tissue that is reached for a quality seal (or evencoagulation), both depend on the characteristics of the tissue clamped,held and/or grasped between the jaw members

$\left( {{e.g.},\frac{1}{\sigma \; \rho \; c}} \right).$

However, it should be noted that calculations of equations (1) and (2)will assume that the pressure exerted on the tissue is evenlydistributed and that during the clamping process the tissue flow islaminar. That is, the tissue does not form any or have any bubblesand/or gaps, while the tissue is grasped between the jaw members.

Taking the above-described phenomena into consideration, the pressureapplied by the electrodes, via the jaw members, plays an important roletowards the changing tissue impedance during a tissue sealing procedurethat ultimately results in a successful tissue seal. Some tissue factorsthat correlate with the amount of pressure applied are, for example, butnot limited to: the amount of volume of tissue; the density of tissue;the viscosity of the tissue; and the specific heat of the tissue. Morespecifically, the amount or volume of tissue grasped by the jaw members(e.g., the electrodes) determines the amount of tissue contact theelectrodes require and the distance between the electrodes. With regardto tissue density, the density of tissue grasped relates to pressurebecause if the jaws exert a very high pressure, the stress limit of thetissue may be exceeded, thus bursting and/or rupturing a majority ofcells of the tissue. Knowing or measuring the overall viscosity of thetissue is important during clamping of the jaws because discontinuitiesmay cause turbulent flow that would cause unwanted bubbles or gaps.Specific heat of the tissue relates to: the pressure applied during theapplication of pressure on tissue; the changes in cell shape; and/orrupturing may affect the specific heat in some way.

Another issue that may arise during electrosurgical surgery is “arcing”between electrodes. Arcing, which is also commonly referred to aselectrical arcing, is an electrical breakdown of a gas which produces anongoing plasma discharge that results from a current flowing throughnonconductive media, for example, air. Some factors that affect arcingare the so-called “clearance distance” and the so-called “creepagedistance” between the electrodes. The clearance distance is the shortestdistance between two conductive media measured through air. Duringsurgery, air clearance is of concern as high transient voltages can arcover or breach a dielectric barrier. The creepage distance is theshortest path between two conductive media measured along the surface ofnonconductive media. Given a high enough potential applied between twopoints on nonconductive media, the right environmental conditions, andsufficient time, the surface of the nonconductive media may break downresulting in an arc between conductive surfaces. This is called“tracking.” Tracking occurs only with surfaces and is not typicallyassociated across air.

SUMMARY

The present disclosure relates to an electrode assembly for use with anelectrosurgical instrument. The electrode assembly includes a pair ofopposing jaw members and an electrode positioned on each jaw member. Oneor both of the electrodes includes a tissue contacting surface that hasan outer periphery and defines a side surface depending therefrom. Thetissue contacting surface and the side surface include a conjoining edgeformed at a first predetermined angle that defines a first lineartransition zone dimensioned to simultaneously reduce arcing between theopposing jaw members during activation of the electrosurgical instrumentand maintain laminar flow of the tissue during clamping.

In one embodiment, the conjoining edge of one or both of the electrodesis formed by the first predetermined angle to define the first lineartransition zone and a second predetermined angle to define a secondlinear transition zone.

In embodiments, the conjoining edge may be calculated from a hyperbolicequation, a parabolic equation, exponential equation, a clothoidequation, Bernoulli's equation, or an Archimedean equation.

In embodiments, the conjoining edge of one or both of the electrodes mayinclude a chamfered configuration that defines an angle relative to thetissue contacting surface. The angle may be about 5 degrees to about 10degrees.

The present disclosure also relates to a method for manufacturing anelectrode assembly for use with an electrosurgical instrument. Themethod includes providing an electrode assembly having a pair ofopposing jaw members and an electrode positioned on each jaw member. Oneor both of the electrodes includes a tissue contacting surface that hasan outer periphery that defines a side surface depending therefrom. Inanother step, a conjoining edge if formed at a first predetermined anglerelative to and disposed between the tissue contacting surface and theside surface. The conjoining edge defines a linear transition zonedimensioned to simultaneously reduce arcing between opposing jaw membersduring activation of the electrosurgical instrument and maintain laminarflow of the tissue during clamping.

In embodiments, the forming of the conjoining edge may be calculatedfrom a hyperbolic equation, a parabolic equation, exponential equation,a clothoid equation, Bernoulli's equation, or an Archimedean equation.

In embodiments, the forming of the conjoining edge may include theformation of a second predetermined angle that defines a second lineartransition zone. The first and second linear transition zones may alsobe calculated from the equations consisting of a hyperbolic equation, aparabolic equation, exponential equation, a clothoid equation,Bernoulli's equation, or an Archimedean equation.

In embodiments, another method for manufacturing an electrode assemblyincludes providing an electrode on a jaw member that includes a sidesurface having a vertical configuration relative to the jaw member and atissue contacting sealing surface having a horizontal configurationrelative to the jaw member. In another step, the edges of the electrodeare chamfered at a predetermined angle relative to the side edges andthe inner facing sealing surfaces. The chamfered edges are configured toreduce a width of the inner facing sealing surfaces and create a lineartransition zone to reduce arcing between opposing jaw members. The stepof chamfering may include cutting or molding. In embodiments, thepredetermined angle may be about 5 degrees to about 10 degrees.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiment of the subject instrument are described herein withreference to the drawings wherein:

FIG. 1A is a perspective view of an endoscopic forceps having anelectrode assembly in accordance with an embodiment of the presentdisclosure;

FIG. 1B is a perspective view of an open forceps having an electrodeassembly in accordance with an embodiment according to the presentdisclosure;

FIG. 2A is a front, cross-sectional view of a prior art electrodeassembly showing a schematically-illustrated electric field plot;

FIG. 2B is a front, cross-sectional view of the prior art electrodeassembly of FIG. 2A showing a schematically-illustrated tensor plot oftissue flow during clamping of a tissue;

FIG. 3A is a front, cross-sectional view of an electrode assembly inaccordance with an embodiment of the present disclosure showing aschematically-illustrated electric field plot;

FIG. 3B is a front, cross-sectional view of the electrode assembly ofFIG. 3A showing a schematically-illustrated tensor plot of tissue flowduring clamping of a tissue;

FIG. 4A is a front, cross-sectional view of another electrode assemblyin accordance with an embodiment of the present disclosure showing aschematically-illustrated electric field plot;

FIG. 4B is a front, cross-sectional view of the electrode assembly ofFIG. 4A showing a schematically-illustrated tensor plot of tissue flowduring clamping of a tissue;

FIG. 5 is an enlarged view of the area of detail of the electrode ofFIG. 4A;

FIG. 6 is a front, cross-sectional view of an electrode in accordancewith an embodiment of the present disclosure schematically-illustratinga graphical plot superimposed thereon; and

FIG. 7 is a front, cross-sectional view of an electrode in accordancewith another embodiment of the present disclosureschematically-illustrating a graphical plot superimposed thereon.

DETAILED DESCRIPTION

Embodiments of the presently-disclosed electrosurgical instrument aredescribed in detail with reference to the drawings wherein likereference numerals identify similar or identical elements. As usedherein, the term “distal” refers to that portion which is further from auser while the term “proximal” refers to that portion which is closer toa user. As used herein, the term “easement” refers to a portion of anelectrode that is between a tissue contacting surface and a side surfaceof the electrode, which will be described in greater detail below.

In accordance with embodiments of the present disclosure, an electrodeassembly may be manufactured wherein each electrode includes a so-calledeasement or linear transition zone to facilitate a uniform currentdensity distribution to a portion of the electrode assembly and ensurelaminar tissue flow when the electrode assembly is grasping tissue. Inthis manner, during tissue treatment (e.g., coagulation or sealing) ofbody tissue, unintended side effects to treated tissue and surroundinguntreated tissue is substantially reduced. The easement of eachelectrode may be configured at an angle that may be derived empiricallyand/or by various embodiments of novel methods that will be describedherein. In one embodiment, a method of manufacturing the easement iscalculated by finite element analysis using homogeneous tissue models orother suitable tissue models that include both electrical and mechanicalproperties. In another embodiment, a method of manufacturing theeasement is calculated by estimating an angle between the horizontal andside surfaces based on an approximation for a homogeneous tissue model(e.g., may be about 5 degrees to about 10 degrees, assuming the efficacyis dependent on a tangent function of the jaw members).

The present disclosure also provides electrodes that are configured toavoid so-called “hot spots” of high current density and/or contactpoints that may allow an arc to form on or between the electrodes.Essentially, an easement may be provided between the tissue contactingsurface and the side surface of the electrode to substantially reducethese “hot spots” or discontinuities.

One advantage in providing easements on electrodes, in particular whenprovided on larger electrodes, is that easements provide a gradualchange (e.g., a smooth transition) along the dimension of the electrode.For example, the tissue contacting surface may transition to the sidesurface via an easement (e.g., a calculated curve) rather than astraight edge (e.g., corner), as shown in FIG. 2A. In this manner, thechange in the electric field density (as shown in FIG. 4A) between theelectrode edges travels through a linear transition zone (e.g.,easement), rather than abrupt changes in electric field densityassociated with squared edges (as shown in FIG. 2A). FIGS. 2A-4Billustrate a schematic of electric field contour lines 132, 232 and 332,stress tensors 136 and 236 of tensor field plots 135, 235 and 335 andlaminar tissue flow tensors 138, 238 and 338 during clamping or graspingof tissue for each of the configurations discussed below.

Referring now to the figures, FIG. 1A depicts an endoscopic forceps 10as used in correlation with endoscopic surgical procedures and FIG. 1Bdepicts an open forceps 10′ as used in correlation with open surgicalprocedures. For the purposes herein, either an endoscopic instrument oran open surgery instrument may be utilized with the novel electrodeassembly described herein. It should be noted that different electricaland mechanical connections and other considerations may apply to eachparticular type of instrument. However, the novel aspects with respectto the electrode assembly described herein and the operatingcharacteristics thereof remain generally consistent with respect to boththe endoscopic or open surgery designs.

The forceps 10 is coupled to an electrosurgical energy source andadapted to seal tissue using radiofrequency (RF) energy. Theelectrosurgical energy source (e.g., generator 40) is configured tooutput various types of energy such as RF energy having a frequency fromabout 200 KHz to about 5000 KHz. Forceps 10 is coupled to generator 40via a cable 34 that is adapted to transmit the appropriate energy andcontrol signals therebetween.

Forceps 10 is configured to support an electrode assembly 200. Forceps10 typically includes various conventional features (e.g., a housing 20,a handle assembly 22, a rotating assembly 18, and a trigger assembly 30)that enable a pair of jaw members 210 and 220 to mutually cooperate tograsp or clamp, seal and divide tissue. Handle assembly 22 includes amoveable handle 24 and a fixed handle 26 that is integral with housing20. Handle 24 is moveable relative to fixed handle 26 to actuate the jawmembers 210 and 220 via a drive rod (not shown) to grasp and treattissue. Forceps 10 also includes a shaft 12 that has a distal portion 16that mechanically engages electrode assembly 200 and a proximal portion14 that mechanically engages housing 20 proximate rotating assembly 18disposed on housing 20. Rotating assembly 18 is mechanically associatedwith shaft 12 such that rotational movement of rotating assembly 18imparts similar rotational movement to shaft 12 which, in turn, rotateselectrode assembly 200.

Electrode assembly 200 includes jaw members 210 and 220 each having anelectrode 212 and 222, respectively, associated therewith and on aninner facing surface thereof. One or both of the jaw members 210 and 220are pivotable about a pin 19 and are movable from a first position suchthat jaw members 210 and 220 are spaced relative to another, to a secondposition such that jaw members 210 and 220 are closed and cooperate toclamp or grasp tissue therebetween. As discussed in more detail below,electrode assembly 200 is adapted for use with an RF energy source.

Electrodes 212 and 222 are connected to generator 40 and configured tocommunicate electrosurgical energy through tissue held therebetween.Electrodes 212 and 222 cooperate to grasp, coagulate, seal, cut, and/orsense tissue held therebetween upon application of energy from generator40.

Trigger assembly 30 is configured to actuate a knife (not shown)disposed within forceps 10 to selectively sever tissue that is graspedbetween jaw members 210 and 220. Switch assembly 32 is configured toallow a user to selectively provide electrosurgical energy to electrodeassembly 100. A cable 34 connects the forceps 10 to generator 40 thatprovides electrosurgical energy (e.g., RF energy) to the jaw members 210and 220 through various conductive paths and ultimately to electrodeassembly 200.

Referring now to FIG. 1B, an open forceps 10′ is depicted and includeselectrode assembly 200 (similar to forceps 10) that is attached to ahandle assembly 20′ having a pair of elongated shaft portions 12 a′ and12 b′. Each elongated shaft portion 12 a′ and 12 b′ has a proximal end14 a′ and 14 b′, respectively, and a distal end 16 a′ and 16 b′,respectively. Similar to forceps 10, electrode assembly 200 includes jawmembers 210 and 220 that attach to distal ends 16 a′ and 16 b′ of shafts12 a′ and 12 b′, respectively. Jaw members 210 and 220 are connectedabout a pivot pin 19′ that allows jaw members 210 and 220 to pivotrelative to one another from the first to second positions for treatingtissue (as described above).

Each shaft 12 a′ and 12 b′ includes a handle 17 a′ and 17 b′,respectively, disposed at the proximal end 14 a′ and 14 b′ thereof.Handles 17 a′ and 17 b′ facilitate movement of the shafts 12 a′ and 12b′ relative to one another which, in turn, pivot the jaw members 210 and220 from an open position such that the jaw members 210 and 220 aredisposed in spaced relation relative to one another to a clamped orclosed position such that the jaw members 210 and 220 cooperate to grasptissue therebetween.

Forceps 10′ includes a trigger assembly 30′ (similar to forceps 10) thatis configured to actuate a knife (not shown) disposed within shaft 12b′. The knife is configured to allow a user to selectively sever tissuethat is grasped between jaw members 210 and 220. One or more of theshafts, e.g., shaft 12 a′, includes a switch assembly 32′ (similar toforceps 10) that is configured to allow a user to selectively provideelectrical energy to the electrode assembly 200. In a similar fashion toforceps 10, cable 34′ of forceps 10′ is internally divided within theshaft 12 b′ to transmit electrosurgical energy through variousconductive pathways to the components of electrode assembly 200.

Referring now to FIGS. 2A and 2B, a traditional prior art electrodeassembly is shown having a schematic electric field plot 130 (FIG. 2A)and a tensor field plot 135 of turbulent flow of tissue (FIG. 2B)illustrated thereon. Traditional electrode assembly 100 includes jawmembers 110 and 120 each having sealing electrodes 112 and 122 disposedon an inwardly-facing surface thereof that each have an outer adjoiningedge (e.g., edge 111) formed by the intersection of side surface (e.g.,side surface 112 a) and the respective sealing surface (e.g., sealingsurface 112 b). Edge 121 is formed in the same fashion at theintersection of side surface 112 a and sealing surface 122 b. The angle“a” defined by the adjoining surfaces, namely, 112 a, 112 b and 122 a,122 b, respectively, is about 90 degrees.

As shown by the electric field distribution near the edges 111 and 121of FIG. 2A, this particular end effector 100 configuration tends toproduce high current concentration at these edges which can lead toelectric field fringing because of the square-shaped configuration ofelectrodes 110 and 120. Prior art electrodes 110 and 120 may alsoproduce a high concentration of electric field lines 132 and a highconcentration of electrical charge at their respective corners 111 and121 and/or respective surfaces 112 a, 122 a and 112 b, 122 b. Thecombination of high concentration of electric field lines, highconcentration of electrical charge of the square-shaped configuration ofelectrodes 110 and 120 may induce unintended electrical arcing betweensealing electrodes 110 and 120 and may lead to undesired tissue effects.As discussed above, tissue burn is calculated using the Arrheniusfunction (2), where “Ω” is a dimensionless burn parameter (e.g., whenΩ=1, a first degree burn is present). An electric field plot 130 of atraditional electrode assembly 130 shows a high degree of energyconcentration (e.g., electric field lines 132) at corners 111 and 112that may produce arcing.

Referring now to FIG. 2B, surface discontinuities may occur anywhere onelectrode assembly 100. For example, surface discontinuities may occurat sharp corners (e.g., edges 111 and 121) of the electrodes 112 and 122and can induce turbulent flow within the tissue being extruded causinghigh stress tensors 136 that could potentially damage (e.g., shred)tissue cells, as shown in tensor field plot 135. In this configuration,laminar flow within tissue is limited to a region 138 between sealingsurfaces 112 b and 122 b.

Turning now to FIG. 3A, an electrode assembly 200 is shown in accordancewith an embodiment of the present disclosure (alsoschematically-illustrating a resulting electric field plot 230).Electrode assembly 200 includes jaw members 210 and 220 each having achamfered-edge configuration. The chamfered-edge configuration of eachjaw member may be utilized for construction of small or large jawmembers 210 and 220. Accordingly, jaw members 210 and 220 each includesealing plates or electrodes 212 and 222, respectively, that arechamfered (e.g., angled) at their respective corners 211 c and 222 c.That is, each jaw member 212, 222 includes a side surface 212 a and 222a, respectively, and a sealing surface 212 b, 222 b, respectively, thatmeet along a chamfered edge 212 c, 222 c.

The chamfered configuration 212 c, 222 c may be configured to have anangle “β” that is relative to the respective side edges 212 a and 222 aand inner facing sealing surfaces 212 b and 222 b of jaw members 210 and220, as shown in FIG. 3A. Angle “β” may be any suitable angle, forexample, but not limited from about 5 degrees to about 10 degrees thatmay be derived empirically. By virtue of chamfering (e.g., rounding orcutting off) the corner of the electrode 212, 222, the width of sealingsurfaces 212 b and 222 b is reduced to a distance “d.” In this manner,the surface area of each sealing surface 212 b, 222 b is reduced tomimic a “small jaw surface area.” This method of manufacture facilitatesthe dispersion of energy (e.g., electric field lines 232), thusmitigating unintended hot spots, tissue shredding and/or arcing at theconjoining edges. As shown in FIG. 3A, the chamfered electrodes 212 and222 produce an electric field plot 230 (shown by electric field lines232) that has a lower degree of electric field fringing (when comparedto electric field plot 130), a lower concentration of electric fieldlines 232 at corners that reduces the chance of arcing.

In other embodiments, electrode assembly 200 may be initiallymanufactured such that sealing surface 212 b and 222 b, respectively,have a square-cornered configuration similar to a traditional electrodeassembly 100. Afterwards, during a manufacturing process the corners maybe cut or molded to have the chamfered or rounded configuration 212 cand 222 c, as described above. During use, sealing surfaces 212 b and222 b are configured to be conductive and selectively activated toprovide for the primary sealing surface for when tissue is graspedtherebetween.

Referring now to FIG. 3B, similar to electrode assembly 100, surfacediscontinuities may also occur anywhere on electrode assembly 200. Forexample, surface discontinuities may occur at the chamfered corners(e.g., edges 212 c and 222 c) of the electrodes 212 and 222, which caninduce turbulent flow within the tissue being extruded causing highstress tensors 236 that could potentially damage (e.g., shred) tissuecells, as shown in tensor field plot 235. In this configuration, laminarflow within tissue is limited to a region 238 between sealing surfaces212 b and 222 b.

Referring to FIG. 4A, in accordance with an embodiment of the presentdisclosure a larger electrode assembly 300 is shown. Jaw assembly 300includes jaw members 310 and 320 each having a pair of electrodes 312and 322, respectively. Easements 312 c and 322 c (e.g., lineartransition zones) on electrodes 312 and 322 are included to graduallytransition the side surfaces 312 a, 322 a to the tissue contactingsurfaces 312 b, 322 b (e.g., transitioning from a straight line to acurve).

One advantage in utilizing easement 312 c on an electrode assembly(e.g., electrode assembly 300) is having an overall increase in creepageand clearance distances for arcs to travel. That is, the electrodeassembly 300 can tolerate or accommodate larger voltage potentialsacross the electrodes 310 and 320 before any possible arcing may occurduring tissue treatment.

Another advantage of utilizing an easement or linear transition zone 312c on electrode assembly 300 is the reduction of tissue shredding andother types of tissue damage that may occur where surfacediscontinuities take place on the electrodes during clamping andelectrosurgical treatment. Typically, vascular tissue is a visco-elasticsubstance that is forced to continuously flow therewithin when placedunder a clamping pressure. Surface discontinuities may occur anywhere onthe electrode, typically at sharp corners, which can induce turbulentflow within the tissue being extruded causing high stress tensors thatcould potentially damage (e.g., shred) tissue cells, if the pressurebetween the electrodes reaches a threshold. Thus, by substantiallyeliminating corners or sharp edges on electrodes via easements, highstress tensors at discontinuities will be reduced thereby substantiallyreducing possible introduction of bubbles, gaps or non-homogeneousregions within the tissue. By preventing tissue shredding, electricarcing may be reduced, since shredded tissue may be a potential arcpoint(s).

During a surgical treatment, electrodes may encounter bubble formationand release during heating that can also potentially damage tissue atthe corners and/or edges, if chamfering is not done properly for many ofthe same reasons as the above fluid flow problem. The sharper the cornerof the more acute, and short, chamfers the more possibility foraccumulation of explosive bubbles at any discontinuities (e.g., eddypockets). Explosive bubbles can also char or damage surrounding cellsagain creating potential hot spots and arcing at portions of theelectrodes. During surgical treatment, once a high current density path332 forms within the tissue treating zone, an arc may easily breakthrough any such open spot by either wet or dry tracking and potentiallydamage surrounding tissue.

The novelty of shaping and dimensioning electrodes 312 and 322 to haveeasements 312 c and 322 c reduces the non-linearaties in the electricfield density and the flow of tissue during clamping. That is, thetransition in electric field density and the flow velocities betweenelectrodes 312 and 322 travel through a linear transition zone fromsealing surface 312 b, 322 b to side surface 312 a, 322 a via easements312 c, 322 c. There are various methods of manufacturing easements onelectrodes. Some of these methods include using various formulas toaccurately and precisely configure the easement on an electrode. Varioustechniques and/or equations may be utilized in conjunction with anelectrode manufacturing process to produce one or more easements on anelectrode, such as, a hyperbolic equation, a parabolic equation,exponential equation, a clothoid equation, Bernoulli's equation, anArchimedean equation or any other suitable equation.

Referring now to FIG. 4B, as described above, electrode assembly 300includes linear transition zones or easements 312 c and 322 c thatprovide a gradual transition between tissue contacting surfaces 312 band 322 b and side surfaces 312 a and 312 a. In this configuration,easements 312 c and 322 c also substantially avoid the surfacediscontinuities described above with regard to electrode assemblies 100and 200. In this manner, easements 312 c and 322 c induce laminar flowin most regions of the electrode assembly 300, as shown by laminar flowtensor 338 between tissue contacting surfaces 312 b and 322 b. Easements312 c and 322 c also reduce turbulent flow within tissue around mostedges (e.g., easements 312 c and 322 c) of electrode assembly 300. Thatis, tensors 338 are shown in a linear configuration in tensor field plot335, rather than turbulent high stress tensors (e.g., high stresstensors 136).

FIG. 5 illustrates an enlarged view of electrode 312 of the electrodeassembly 300 having one or more easements or linear transition zones 312c and 312 d. Electrode 312 includes a side surface 312 a, a tissueenergizing electrode surface 312 b, and a conjoining edge. Theconjoining edge is formed by a first predetermined angle to define afirst linear transition zone or easement 312 c and by a secondpredetermined angle to define a second linear transition zone oreasement 312 d.

FIG. 6 illustrates a portion of an electrode assembly in accordance withan embodiment of the present disclosure having a graphical plotsuperimposed thereon. One embodiment disclose herein describes a methodof manufacturing an easement on an electrode and includes providing aclothoid spiral equation (e.g., a Euler Spiral) to determine theposition of the easement on the individual electrode. An example of aclothoid spiral equation includes the following Fresnel integrals:

$\begin{matrix}{x = {+ {\int_{0}^{A}{{\cos \left( {\frac{\pi}{2}s^{2}} \right)}{ds}}}}} & (3) \\{y = {- {\int_{0}^{A}{{\sin \left( {\frac{\pi}{2}s^{2}} \right)}{ds}}}}} & (4)\end{matrix}$

where s is the arc length of the line 400.

In this embodiment, electrode 412 includes a vertical tangent or sidesurface 412 a and a tissue engaging sealing surface 412 b, a firsteasement or linear transition zone 412 c and a second easement or lineartransition zone 412 d. By utilizing the clothoid spiral, an easement maybe configured and dimensioned to include a tissue contacting surfaceincluding a sealing surface 412 b having a straight-line configuration(e.g., along the x-axis) and terminating at the origin “0.” From theorigin “0,” easement 412 c is formed along the electrode 412 andcontinues to point “A” along line 400 of electrode 412. At this point, avertical tangent may be formed on side surface 412 a and continue in avertical direction to any suitable length (e.g., along the y-axis).Alternatively, electrode 412 may further include easement 412 d that maybe formed alongside the electrode, for example, from point “A” to point“B.” In this configuration, another vertical tangent or side surface 412a′ may be formed and continue in a vertical direction to any suitablelength from point “B.” Easement 412 d may have a radius equal to thecurvature of coordinates (e.g., x, y) between points “A” and “B” or anyother suitable radius. In any of these embodiments, electrode 412includes the benefits of having easement(s) 412 c, 412 d, as discussedabove with other embodiments.

FIG. 7 depicts a portion of an electrode 510, in accordance with anotherembodiment of the present disclosure having a graphical plotsuperimposed thereon.

In this method of manufacturing, an easement is created on electrode 512by calculating a parabolic equation utilizing angles “Θ” and “φ” shownon FIG. 7. Angle “φ” is the angle of a tangent taken along the tissueenergizing sealing surface 512 b relative to the angled edge 512 d.Angle “Θ” is calculated using equation (3) below. The parabolic equationdetermines the position of the easement on electrode 512. An example ofa parabolic equation includes the following derivations:

$\begin{matrix}{\Theta = \frac{180 - \varphi}{2}} & (3) \\{R_{m} = {\frac{s^{2}}{B} = \left\lbrack \frac{C*{\sin^{2}(\Theta)}}{\cos (\Theta)} \right\rbrack}} & (4) \\{C \cong {R_{m}*\left\lbrack \frac{\cos (\Theta)}{\sin^{2}(\Theta)} \right\rbrack}} & (5)\end{matrix}$

where “C” is the length of vertical side surface 512 a before electrode512 is modified (e.g., cut or chamfered), “R_(m)” is the minimum radius,“S” is the length of the easement, “B” is distance from a midpoint ofthe easement 512 c to a corner of a pre-cut portion of electrode 512that is formed by sealing surface 512 b′ and angled portion 512 d. Inthis embodiment, an easement radius “R_(e)” may be calculated at anypoint along the easement. The equation below may be used to calculateradius “R_(e)”:

$\begin{matrix}{R_{e} \cong {R_{m}*\left\lbrack {1 + \frac{4*x^{2}}{R_{m}^{2}}} \right\rbrack}} & (6)\end{matrix}$

where “R_(e)” is the easement radius, “R_(m)” is the minimum radius and“x” is a predetermined point.

By utilizing the parabolic equation, an easement may be configured anddimensioned to be formed having a length “S” by choosing desired valuedfor “B,” “C,” and/or “R_(m).” These values, as previously described, maybe found by appropriate empirical testing and/or finite elementanalysis.

The above-described calculations may be associated with a manufacturingprocess of electrode assemblies 212, 312, 412 and 512. For example,computer-aided manufacturing machines that are instructed by a softwaremay be programmed to receive instructions on the desired easementspecifications. The software may include any one of the above-describedcalculations for creating an easement on an electrode. In otherexamples, any of the above-described calculations may be manuallyinterpreted by an operator and, subsequently, the electrode may bemodified by any suitable machining process to include easements asdescribed above.

Electrodes may be attached to their respective jaw members by stamping,by overmolding, by casting, by overmolding a casting, by coating acasting, by overmolding a stamped electrically conductive sealing plateand/or by overmolding a metal injection molded seal plate or in otherways customary in the art. All of these manufacturing techniques may beemployed to produce the above-described jaw members and include anelectrically conductive electrode with an easement configuration forcontacting and treating tissue.

While several embodiments of the disclosure have been shown in thedrawings and/or discussed herein, it is not intended that the disclosurebe limited thereto, as it is intended that the disclosure be as broad inscope as the art will allow and that the specification be read likewise.Therefore, the above description should not be construed as limiting,but merely as exemplifications of particular embodiments. Those skilledin the art will envision other modifications within the scope and spiritof the claims appended hereto.

1-18. (canceled)
 19. An electrode for use in an electrosurgicalinstrument, the electrode comprising: a tissue-contacting surface; apair of opposing lateral side surfaces; and an easement interconnectingthe tissue-contacting surface and a first lateral side surface of thepair of opposing lateral side surfaces, the easement including: a firsteasement portion having a radius of curvature and extending laterallyfrom the tissue-contacting surface toward the first lateral sidesurface; and a second easement portion extending between the firsteasement portion and the first lateral side surface.
 20. The electrodeof claim 19, wherein the first easement portion is disposed between thetissue-contacting surface and the second easement portion.
 21. Theelectrode of claim 19, wherein the first lateral side surface extendslinearly along a vertical axis from the second easement portion.
 22. Theelectrode of claim 19, wherein each of the first and second easementportions is convex.
 23. The electrode of claim 22, wherein the secondeasement portion has a radius of curvature that is different than theradius of curvature of the first easement portion
 24. The electrode ofclaim 19, wherein the first easement portion has a first end extendingfrom the tissue-contacting surface and a second end, the second easementportion having a first end extending from the second end of the firsteasement portion and a second end connected to the first lateral sidesurface.
 25. The electrode of claim 19, wherein the first easementportion has a longer circumference than the second easement portion. 26.A method for manufacturing an electrode for use in an electrosurgicalinstrument, the method comprising: forming an easement between a firstlateral side surface of an electrode and a tissue-contacting surface ofthe electrode, the easement having a curved configuration; machining theeasement to form a first easement portion having a radius of curvature,the first easement portion extending laterally from thetissue-contacting surface toward the first lateral side surface; andmachining the easement to form a second easement portion having a radiusof curvature that is different than the radius of curvature of the firsteasement portion.
 27. The method of claim 26, wherein each of the firstand second easement portions is convex.
 28. The method of claim 26,wherein the radius of curvature of at least one of the first easementportion or the second easement portion is calculated from a parabolicequation.
 29. The method of claim 26, wherein the radius of curvature ofat least one of the first easement portion or the second easementportion is calculated from a clothoid equation.
 30. The method of claim26, further comprising machining at least one edge of the electrode toform the easement.
 31. The method of claim 26, wherein the first lateralside surface extends linearly along a vertical axis from the secondeasement portion.